Prior Thread Cutting Devices
In the field of machinery for the textile industry, primarily industrial sewing machines, there exist many types of sewing machines. Principal types are commonly referred to as chainstitch, lockstitch, and overlock. Within these types are many configurations of the bed or the arm of the machine itself. Such configurations are commonly referred to as flatbed, cylinder bed, post bed, and sub frame (e.g. overlock) machines. Many items are common to all of these machines; they employ some form of material feeding device, and a reciprocating needle(s), and all employ the use of thread in order to join materials together and or to cause reinforcement to materials or to apply a decorative stitch.
Certain machines employ one or more needles in order to perform the various types of stitching as described above. For example at times more than one needle is required to create a specific federal stitch type, one example being a type 406.
Such sewing machines are commonly used to sew and create a series of stitches referred to as a seam, and after having created such a seam, it is required to trim the thread(s) of the seam so the sewn work piece can be removed from the machine. This requires the machine operator to use a device such as scissors, or (in most cases) the machine itself will be equipped with some form of thread cutting device. Such thread trimming devices are of various types depending upon the machine itself.
Some of the most common forms of automatic or semiautomatic thread cutting devices that are applied to machines are impact cutters, chain cutters, and underbed thread cutters. Impact cutters are of the type that cause the threads to be severed by a knife edge that impacts the thread against a flat surface. This type of cutter can be applied to most any type of sewing machine, but requires that the series of stitches being created continue to form off the edge of the work piece being sewn. In doing so, a chain of stitches is usually created and remains attached to the work piece. This is often unacceptable as it may interfere with the appearance of the work piece. Impact cutters are most common to overlock and chainstitch machines, which are capable of creating a chain of stitches. Use of an impact cutter on a lockstitch machine is usually not popular, but is possible.
The chain cutter type of thread cutting devices is most popular on chainstitch and overlock type machines. Like the impact cutter, the chain cutter type requires that a series of stitches continue to be created in the form of a chain off the edge of the work piece being sewn. The threads are severed by a shearing type device in the form of a small scissor action type device. This sometimes requires the use of a venturi device to pull the threads into the cutting device. The remaining thread chain is usually still intact with the sewn work piece and can also have an effect on the appearance of the work piece, as mentioned with respect to the impact cutters. The ability to initiate another series of stitches must be accomplished at the edge of the work piece, otherwise the chain of stitches remaining within the machine must be separated. This separation of the needle and looper thread(s) is required if it is desired to initiate a series of stitches at any area of the work piece other than an edge. This applies also to impact cutters.
Another type of thread cutting device is the underbed thread cutter, which is mostly popular with lockstitch type machines. Although underbed cutters have been applied to some chainstitch type machines, as in the case of machines manufactured by Union Special Corp., Kansai Special, Singer, and Juki. The underbed cutters for these machines are applied by the original equipment manufacturer, or in some cases by an after market supplier.